Nucleation and Growth of Brushite in the Presence of Alginate

Abstract

Biomineral formation in vivo is a complex process regulated by functional molecules.Highlighting the mechanisms underlying biomineralization is necessary for a better understanding of in vivo processes and for enhanced in vitro model systems. Here, the effect of alginate and its well-defined oligomers with M-or G-block structure on brushite nucleation and growth is investigated by seeded and unseeded experiments. Growth kinetics were studied by seeded experiments and it was shown that molecular weight and functionality of alginate additives affect the crystal growth rates and the growth mechanisms. Growth retardation was most prominent when G-block additives were present. Growth proceeded by surface nucleation when alginate and G-block oligomers were added in the crystallization medium whereas in the presence of M-block oligomers parabolic rate laws were obtained. By decoupling the seeded and experiments, information was deduced on the effects of additives on brushite nucleation. In the presence of alginate and G-block oligomers nucleation was inhibited, however, M-blocks did not show a similar effect. Possible modes of interactions between the mineral and polymer additives are discussed by the evaluation of final crystal morphologies.

A correlative spatiotemporal microscale study of calcium phosphate formation and transformation within an alginate hydrogel matrix

“…[15] It has previously been shown that alginate, and especially the guluronate residues (Gblocks) which have a high affinity for calcium, have an inhibitory effect on the nucleation (and growth) of calcium phosphate crystals. [16]. Chelation of calcium ions is a likely explanation for the nucleation inhibition, while non-specific interactions between alginate and crystals and specific interactions between Gblocks and active growth sites are probable causes of growth inhibition.…”

“…Considering this inhibitory effect of alginate on the nucleation (and growth) of calcium phosphate, as observed by us and others, we expected that the addition of seed crystals would increase the Ca 2+ consumption rate, as it would not rely on nucleation of new crystals. [16,32] We tested this hypothesis by incorporating 0.2 mass% brushite seed crystals with an average size of 30 µm in alginate containing 300 mM phosphate precursor and monitored gel front velocity and crystal growth. For these samples, one might expect the gel front velocity to be reduced to a larger extent compared to samples without seed crystals, due to an increased consumption of Ca 2+ .…”

“…It is likely that the alginate inhibited the nucleation of brushite, as one would expect this phase to nucleate at a pH-value less than 5. [16,40] As some of the phosphate was consumed in the mineralization process, the buffering capacity of the alginate solution was reduced. Due to the local generation and fast diffusion of H + , the central region of the disc experienced the lowest recorded pH, as can be observed in Figure 10 b and c.…”

“…[15] Further investigation into this phenomena revealed an inhibitory effect of alginate on the growth and nucleation of brushite in the presence of small amounts of alginate. [16] A thorough understanding of CaP formation and transformation processes is essential for both fundamental studies of biomineralization and for the development of synthetic hard tissue engineering scaffold biomaterials. CaP mineralization, although dependent on reaction conditions such as pH and ionic strength, is often dictated by kinetics rather than thermodynamics.…”

Effect of the Addition of Alginate and/or Tetracycline on Brushite Cement Properties

“…Between the natural polymers, sodium alginate has been studied for many biomedical applications because it is biocompatible, biodegradable and able to form hydrogels. Sodium alginate hydrogels can be prepared under mild conditions by ionic crosslinking and shows a structural similarity to the extracellular matrices of living tissues, which leads to use in applications such as the administration of bioactive agents, the healing of wounds and in tissue engineering [ 13 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ].…”